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Posted by D. Sherman on Monday, January 21, 2008 at 01:02:15 :
In Reply to: kick start heater posted by mikeLIny on Sunday, January 20, 2008 at 20:05:06 :
Often all that old small motors need is a good cleaning and fresh oil. They usually have "oilite" porous bronze bearing. The old oil gets gummy after a while. I usually take the motor apart clean the shaft ends, and use brake cleaner lacquer thinner or other strong solvent to wash the gummy old oil out of the bearings. Then re-oil with light oil such as sewing machine or gun oil. While it's apart, check that the brushes have plenty of length and spring left to them and the commutator is good. If the commutator didn't spark and the motor ran smoothly once you gave it a push, it's probably okay electrically. If the brushes are good, a sparking commutator indicates shorted turns on the rotor and the motor is junk. That rarely happens with small motors because they don't get hot enough. In general, the most you should do to a commutator is polish it up with crocus cloth.
I've only once had to "turn" a commutator on a lathe, and that was on a well-worn tool post grinder that ran at very high speed and inhaled grit. A reasonable amount of wear and discoloration on the commutator of a small motor is no problem. More common on heater motors is worn out brushes. If they don't make good contact and the springs are still springy, you probably need brushes. A typical heater motor brush, new, is about 1/2" long. You might be able to get replacements from a motor rebuild shop, or if you can get some that are a little too big, you can file or sand them down to fit. They should slide easily in the brush holders.
Given that your fan runs well once you give it a push, I suspect the brushes are okay and it just needs cleaning and oiling. It's still a good time to check the brushes and replace them if they're getting short.